Tailor-Made Poly(vinylamine) via Purple LED-Activated RAFT Polymerization of N-vinylformamide

Photo-iniferter reversible addition-fragmentation chain transfer (PI-RAFT) polymerization of N-vinylformamide (NVF) is demonstrated by using purple light. PNVFs with predetermined molar masses and narrow molar mass distributions are obtained. High RAFT chain-end fidelity is confirmed by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) and electrospray-ionization time-of-flight mass spectrometry (ESI-TOF-MS), and chain extension experiment. To demonstrate the potential of this approach, an original poly(N-vinylpyrrolidone)-b-poly(N-vinylformamide) (PVP-b-PNVF) diblock copolymer is synthesized and characterized by aqueous size-exclusion chromatography (SEC), asymmetric flow field-flow fractionation (A4F), and ¹ H diffusion-ordered spectroscopy nuclear magnetic resonance (¹ H DOSY NMR). Finally, selective hydrolysis of PNVF block to corresponding pH-responsive poly(N-vinylpyrrolidone)-b-poly(N-vinylformamide) (PVP-b-PVAm) is performed.

Ultrastrong, Chemically Resistant Reduced Graphene Oxide-based Multilayer Thin Films with Damage Detection Capability

Multilayer thin films of graphene oxide (GO) and poly(vinylamine) (PVAm) were deposited via layer-by-layer assembly. Poly(vinylamine) pH was used to tailor film thickness and GO layer spacing. Graphene oxide concentration in the films was controlled through simple pH adjustment. Thermal reduction of the PVAm/GO multilayer thin films rendered them electrically conductive, which could be further tailored with PVAm pH. These reduced films also exhibited exceptionally high elastic modulus of 30 GPa and hardness of 1.8 GPa, which are among the highest of any graphene-filled polymer composite values ever reported. Cross-linking of these films with glutaraldehyde improved their chemical resistance, allowing them to survive strongly acidic or salty solutions. Additionally, scratches in the films can be instantaneously detected by a simple electrical resistance measurement. These films are promising for a variety of packaging and electronic applications.